Researchers report that they may have hit on a new trick for weight loss: To eat less of a certain food, they suggest you fantasize about it before you eat it.

Scientists showed day dreaming of a delicious meal actually reduces one's desire for it. But the trick is to visualise gorging non-stop on the food, rather than conjuring up an appetite-whetting single image.

Repeatedly imagining the consumption of a food reduces one's appetite for it at that moment, said lead researcher Carey Morewedge, an assistant professor of social and decision sciences at Carnegie Mellon University in Pittsburgh.

"Most people think that imagining a food increases their desire for it and whets their appetite. Our findings show that it is not so simple," she said.

Thinking of a food -- how it tastes, smells or looks -- does increase our appetite. But performing the mental imagery of actually eating that food decreases our desire for it, Morewedge added.

For the study, published in the Dec. 10 issue of Science, Morewedge's team conducted five experiments. In one, 51 individuals were asked to imagine doing 33 repetitive actions, one at a time. A control group imagined putting 33 coins into a washing machine. Another group imagined putting 30 quarters into the washer and eating three M&Ms. A third group imagined feeding three quarters into the washer and eating 30 M&Ms.

The individuals were then invited to eat freely from a bowl of M&Ms. Those who had imagined eating 30 candies actually ate fewer candies than the others, the researchers found.

To be sure the results were related to imagination, the researchers then mixed up the experiment by changing the number of coins and M&Ms. Again, those who imagined eating the most candies ate the fewest.

In three additional experiments, Morewedge's group confirmed that imagining the eating reduced actual consumption through a process known as habituation. Simply thinking about the food repeatedly or imagining eating a different food did not significantly influence consumption, the researchers also found.

This simulation technique might also help reduce cravings for unhealthy foods and drugs, the authors say.

However, at least one expert had reservations about the findings.

"This small study may offer insights for further research, but the message is not that we can think ourselves thin or reduce food cravings by repeatedly imagining eating a certain food," said Samantha Heller, clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital in Derby, Conn.

It was not in the scope of the study to examine how long the effect described lasted, but it is important to consider, she said. Was it five minutes? Two days? Were the participants hungry during one part of the study but not during another arm of the experiment? And were they normal weight, overweight or underweight, she asked.

"All these factors, and many more, could affect how someone responds to repeatedly imagining eating a certain food," Heller said.

Overweight or obese people may have very different psychological and biochemical responses to this simulation approach compared with normal-weight individuals, she noted.